Studies in this application will test the hypothesis that variation in susceptibility for developing lung cancer is mediated by germ-line polymorphisms in DNA repair genes that compromise repair capacity. This damage in turn leads to the acquisition of epigenetic changes in the form of aberrant gene promoter hypermethylation in critical regulatory genes and malignant transformation. This hypothesis will be tested through four specific aims. In Aim 1 siRNA will be used to reduce expression of genes involved in the nonhomologous recombination and nucleotide excision repair pathways in immortalized bronchial epithelial cells. The effect of reduced gene expression will be assessed by quantifying chromosome aberrations formed following exposure to carcinogens that induce either single- (BPDE1) or double-strand breaks (bleomycin) in DNA. In Aim 2 immortalized bronchial epithelial cell lines with stable knock down of genes found to effect DNA repair capacity (DRC) will be exposed chronically to BPDE1 or bleomycin. Time to transformation and genes inactivated by methylation in these cell lines will be defined and compared to repair competent cell lines. In Aim 3 a nested, case-control study of squamous cell carcinoma (SCC) will be conducted in 1440 radon-exposed uranium miners. Genes identified in Aim 1 to affect DRC will be studied. Global association of each selected locus with SCC risk will be studied using a haplotype approach. Risk variants will be defined and the association of radon dose between cases and controls with specific risk variants investigated. Aim 4 will focus on the elucidation of genes and pathways involved in the development of SCC and whether the genes affected by methylation differ as a function of radon exposure. These studies are relevant to the mission of the NIEHS and NCI: they will uncover the contribution of single- and double-strand break DNA damage associated with environmental carcinogens to lung cancer and identify biomarkers for risk assessment and early detection of lung cancer, the leading cause of cancer-related death in the U.S. PUBLIC HEALTH RELEVANCE: Studies in this application will identify biomarkers for risk (DNA repair genes) and early detection (methylated genes) of lung cancer. Population-based screening studies will then be conducted to evaluate the ability of the biomarker to detect early lung cancer. Ultimately approaches could be developed that modify the activity of the affected genes to prevent or treat lung cancer. 7. Project Narrative These studies will identify biomarkers for risk (DNA repair genes) and early detection (methylated genes) of lung cancer. Population-based screening studies will then be conducted to evaluate the ability of the biomarker to detect early lung cancer. Ultimately approaches could be developed that modify the activity of the affected genes to prevent or treat lung cancer.